Capturing OpenGL Rendered window using OpenCV

When working with graphics I wanted to store whatever was on the output of my OpenGL render window as a set of images. Typically this is achieved by using glReadPixels to read the pixels in the rendered window and store them into a byte array. This array is then converted and saved using a helper library.

I thought of doing the same thing, however, since I am more familiar with OpenCV, I wanted to use cv::Mat to do this.

Turns out it is really straight foward, all you need to do is to initialize the Mat with the required size and store the data directly onto its data container. Here is the code:

//Get dimensions of the image
RECT dimensions = rGameWindow.GetDimensions();
int width = dimensions.right - dimensions.left;
int height = dimensions.bottom - dimensions.top; 

// Initialise a Mat to contain the image
cv::Mat temp = cv::Mat::zeros(height, width, CV_8UC3); cv::Mat tempImage;   

// Read Image from buffer
glReadPixels(0,0, width, height, GL_RGB, GL_UNSIGNED_BYTE,temp.data);

// Process buffer so it matches correct format and orientation
cv::cvtColor(temp, tempImage, CV_BGR2RGB); 
cv::flip(tempImage, temp, 0);

// Write to file
cv::imwrite("savedWindow.png", temp);

Thats all! You do need to do some data conversions to match the format of OpenCV images, but its pretty straightforward and self explanatory.

Implementing SnakesGame using OpenCV

 

A long time back I used to have a nokia phone which came with this awesome and simple game. I still love nokia phones for this, and have a couple of phones just to play it (no kidding, haha). A while back I decided that I will write my own snakes game implementation, so I did. What is interesting about this post is that I did not use any graphics engine or OpenGL rendering at all. Instead this whole game was implemented using OpenCV function calls, enabling me to make my own rendering funcitons and display buffers.

Setting up freeglut and GLTools with Visual Studio 2010

It's good to be writing a tutorial after a long time and there are a number of reasons for that. First of all, I have been really busy with a lot of work and research (well actually I still am!). On the other hand, it is only until recently that I have been struggling with a setup which has little tutorials documented, while there seems to be a lot of beginner developers facing the same problem as I am.

This particular tutorial deals with setting up a Microsoft Visual C++ 2010 Project for use with examples found in the OpenGL Superbible 5th Edition. The book has a section which details the same process for a Visual C++ 2008 project, which is completly different than this tutorial. As always, I have tried to keep everything simple and straightforward so even a person who has no knowledge about these settings can make them work.